This invention relates generally to an improvement in printed circuit boards which are fabricated from, for example, a polyimide dielectric material. More particularly, this invention relates to an improvement in the invention disclosed in the aforenoted U.S. application Ser. No. 319,439, and which disclosure is incorporated herein by reference.
Prior to the invention of U.S. application Ser. No. 319,439, heat generated by electronic and electrical components was dissipated by employing at least one or, more usually, a combination of conduction, radiation and convection techniques. The aforenoted patent application teaches improved high resolution circuit density, copper/polyimide type, multilayer, surface mount, printed circuit boards, and further discloses a modification in the process of U.S. application Ser. No. 2,545, filed on Jan. 12, 1987 (now abandoned), and which disclosure is also incorporated herein by reference.
In the prior art, a metal substrate is provided to produce a high circuit density printed circuit board supported by the metal substrate which is capable of dissipating large amounts of heat. The printed circuit board is generally fabricated by applying a first layer of radiation curable dielectric material to the substrate. A photomask is thereafter disposed to define the conductor circuit patterns adjacent the surface of the radiation curable dielectric material. The material is exposed to a source of radiation and developed to expose those regions of the substrate where a first conductor circuit pattern is to be formed, as by photoimaging. Thereafter, the conductor circuit pattern is formed on the surface of the substrate by plating a metal coating onto those regions of the substrate covered by the exposed layer of the first layer of the curable dielectric material to provide a printed circuit board of which the first layer of the dielectric material is a structural component. The details of manufacturing circuit boards in accordance therewith is well disclosed in the aforenoted U.S. application Ser. No. 319,439 and is disclosed herein only to the extent required for purposes of describing the present invention.
In accordance with the aforenoted U.S. application Ser. No. 319,439, a polyimide dielectric material is processed so that wells for active components such as integrated circuits (ICs) are provided as the circuit pattern is being laid down through the disclosed process. Further, coaxial leads are buried in the polyimide dielectric to connect to ICs mounted in the wells.